Method of manufacturing a three-dimensional object

ABSTRACT

A three-dimensional object may be manufactured using a powder bed fusion additive manufacturing technique. A layer of powder feed material may be distributed over a solid substrate and scanned with a high-energy laser beam to locally melt selective regions of the layer and form a pool of molten feed material. The pool of molten feed material may be exposed to gaseous nitrogen, carbon, or boron to respectively dissolve nitride, carbide, or boride ions into the pool of molten feed material to produce a molten nitrogen, carbon, or boron-containing solution. The molten nitrogen, carbon, or boron-containing solution may cool and solidify into a solid layer of fused nitride, carbide, or boride-containing material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.15/977,545 filed on May 11, 2018, which is hereby incorporated byreference in its entirety.

INTRODUCTION

Nitride, carbide, and borides of metals and non-metals are an attractiveclass of materials due to their wide range of mechanical, electrical,thermal, and magnetic properties.

SUMMARY

A three-dimensional object made of a bulk nitride, carbide, orboride-containing material may be manufactured using a powder bed fusionadditive manufacturing technique. In step (a), a powder feed materialmay be provided. In step (b), a layer of the powder feed material may bedistributed over a solid substrate. In step (c), selective regions ofthe layer of the powder feed material may be scanned with a high-energylaser beam to locally melt the selective regions and form a pool ofmolten feed material. The selective regions of the layer may correspondto a cross-section of a three-dimensional object being formed. In step(d), the pool of molten feed material may be exposed to gaseousnitrogen, carbon, or boron to respectively dissolve nitride, carbide, orboride ions into the pool of molten feed material to produce a moltennitrogen, carbon, or boron-containing solution. In step (e), the laserbeam may be terminated to cool and solidify the molten nitrogen, carbon,or boron-containing solution into a solid layer of fused nitride,carbide, or boride-containing material. Steps (b) through (e) may berepeated to form a three-dimensional object made up of a plurality ofsolid layers of fused nitride, carbide, or boride-containing material.

In step (d), a gas stream may be directed at the pool of molten feedmaterial. The gas stream may comprise at least one of urea (CO(NH₂)₂),ammonia (NH₃), nitrogen (N₂), or methane (CH₄).

Steps (b) through (f) may be performed within a chamber. In such case,in step (d), a nitrogen, carbon, or boron-containing gas may beintroduced into the chamber. In one form, a high-pressure environmentmay be established within the chamber, which may exhibit at a pressurein the range of 150 kPa to 150 MPa. In another form, a subatmosphericpressure environment may be established within the chamber and anelectric field may be generated within the chamber to ionize thenitrogen, carbon, or boron-containing gas and transform the gas into aplasma. In addition, an electric potential difference may be establishedbetween the solid substrate and the plasma to attract nitrogen ions,carbon ions, or boron ions to the pool of molten feed material.

When the selective regions of the layer are scanned with the laser beam,a volume of solid material underlying the selective regions of the layermay not melt and may be maintained at a temperature less than 500° C. Insuch case, upon termination of the laser beam, the pool of molten feedmaterial may be quenched by heat transfer from the pool of molten feedmaterial to the volume of solid material underlying the selectiveregions of the layer.

Upon termination of the laser beam, the pool of molten feed material maybe cooled at a rate in the range of 10⁴ Kelvin per second to 10⁶ Kelvinper second.

During formation of the plurality of solid layers of fused nitride,carbide, or boride-containing material, thermal gradients may berepeatedly generated within the solid layers such that thethree-dimensional object made up of the plurality of solid layersexhibits localized regions of residual stress.

The powder feed material may comprise at least one element selected fromthe group consisting of iron (Fe), titanium (Ti), and silicon (Si). Insuch case, each particle of the powder feed material may comprise the atleast one element in an amount, by weight, greater than or equal to 90%.The powder feed material also may comprise at least one nonmetal elementselected from the group consisting of nitrogen, carbon, or boron. Insuch case, each particle of the powder feed material may comprise the atleast one nonmetal element in an amount, by weight, less than or equalto 5%.

In one form, the powder feed material may comprise iron (Fe), the poolof molten feed material may be exposed to gaseous nitrogen in step (d)to produce a molten solution of iron and nitrogen, and thethree-dimensional object formed in step (f) may be a permanent magnetmade up of a plurality of solid layers of fused iron nitride material.The iron nitride material may comprise a magnetic Fe₁₆N₂ phase. The ironnitride material may comprise, on an atomic basis, greater than 10%nitrogen and the magnetic Fe₁₆N₂ phase may exhibit a body-centeredtetragonal (bct) crystal structure. During formation of the plurality ofsolid layers of fused iron nitride material, thermal gradients may berepeatedly generated within the solid layers such that thethree-dimensional object exhibits localized strains in the range of 0.5%to 1%. The localized strains may promote formation and stabilization ofthe magnetic Fe₁₆N₂ phase.

In another form, the powder feed material may comprise an alloy of iron(Fe) and carbon (C), the pool of molten feed material may be exposed togaseous nitrogen or carbon in step (d), and the three-dimensional objectformed in step (f) may be made up of a plurality of solid layers ofhardened steel. The hardened steel may exhibit a body-centered cubiccrystal structure or a face-centered cubic crystal structure and maycomprise, by weight, 0.1% to 4% carbon and 0.01% to 0.5% nitrogen.

The three-dimensional object may comprise a solid exterior and a porousinterior enclosed within the solid exterior.

After step (f), the three-dimensional object may be exposed to gaseousnitrogen, carbon, or boron to increase the respective concentration ofnitrogen, carbon, or boron within the solid layers of fused nitride,carbide, or boride-containing material. In such case, thethree-dimensional object may comprise a plurality of flow-throughchannels defined by walls having wall surfaces and the gaseous nitrogen,carbon, or boron may be directed through the flow-through channels inthe three-dimensional object such that the gaseous nitrogen, carbon, orboron contacts the wall surfaces and promotes dissolution of nitride,carbide, or boride ions into the solid layers of fused nitride, carbide,or boride-containing material.

A three-dimensional permanent magnet may be manufactured using a powderbed fusion additive manufacturing technique. In step (a), an iron-basedpowder feed material may be provided. In step (b), a layer of the powderfeed material may be distributed over a solid substrate. In step (c),selective regions of the layer of the powder feed material may bescanned with a high-energy laser beam to locally melt the selectiveregions and form a pool of molten feed material. The selective regionsof the layer may correspond to a cross-section of a three-dimensionalobject being formed. In step (d), the pool of molten feed material maybe exposed to gaseous nitrogen to dissolve nitride ions into the pool ofmolten feed material. In step (e), the laser beam may be terminated tocool and solidify the pool of molten feed material into a solid layer offused iron nitride material. In step (f), steps (b) through (e) may berepeated to form a three-dimensional object made up of a plurality ofsolid layers of fused iron nitride material. The fused iron nitridematerial may comprise, on an atomic basis, greater than 10% nitrogen. Inaddition, the fused iron nitride material may comprise a magnetic Fe₁₆N₂phase exhibiting a body-centered tetragonal (bct) crystal structure.

During formation of the plurality of solid layers of fused iron nitridematerial, thermal gradients may be repeatedly generated within the solidlayers such that the three-dimensional object exhibits localized strainsin the range of 0.5% to 1%. The localized strains may promote formationand stabilization of the magnetic Fe₁₆N₂ phase.

The three-dimensional object may be V-shaped, W-shaped,trapezoid-shaped, or helical in shape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic perspective view of an apparatus for manufacturingthree-dimensional objects made of bulk nitride, carbide, and/orboride-containing materials using a powder bed fusion additivemanufacturing technique, in accordance with one embodiment of thepresent disclosure; and

FIG. 2 is a magnified view of a laser beam impinging upon a layer ofpowder feed material distributed over a previously melted, fused, andsolidified layer of feed material on a building platform of theapparatus of FIG. 1 .

DETAILED DESCRIPTION

In the presently disclosed methods, a powder bed fusion additivemanufacturing technique is used to build up three-dimensional objectsmade of bulk nitride, carbide, and/or boride-containing materials byintroducing nitride, carbide, and/or boride ions into a transient volumeof molten feed material that is produced as a high-energy laser beamscans selective regions of a powder feed material layer to fuse theregions into a one-piece unitary structure. In one form, athree-dimensional object made of a bulk iron nitride material may beproduced that includes a relatively high concentration of nitrogen(e.g., greater than 10 at %) and exhibits a magnetic Fe₁₆N₂ phase. Insuch case, thermal gradients generated within the three-dimensionalobject during manufacture thereof may lead to local residual stresses inthe object that help promote formation and stabilization of the magneticFe₁₆N₂ phase. In another form, a three-dimensional object made of a bulkiron (Fe), titanium (Ti), or silicon (Si)-based material may be producedthat includes a relatively low concentration of nitride, carbide, and/orboride ions (e.g., less than 5 wt %). In such case, the nitride,carbide, and/or boride ions may be dissolved in solid solution with theiron (Fe), titanium (Ti), or silicon (Si) and may help increase thestrength of the bulk iron (Fe), titanium (Ti), or silicon (Si)-basedmaterial.

FIG. 1 depicts an apparatus 10 that can be used to manufacture athree-dimensional object 12 made of a bulk nitride, carbide, and/orboride-containing material using a powder bed fusion additivemanufacturing technique in which digital design data is used to build upthe object 12 layer by layer. The apparatus 10 depicted in FIG. 1 isconfigured to build up the object 12 using a selective laser meltingtechnique and includes a building chamber 14 including a buildingplatform 16, a powder feed material reservoir 18 separated from thebuilding chamber 14 by a weir 20, and a high-power laser beam source 22.The apparatus 10 may be enclosed within a chamber 24. The chamber 24 mayinclude an inlet 26 coupled to a source of gaseous nitrogen, carbon,and/or boron 28 and an outlet 30 coupled to a vacuum pump and evacuationsystem 32.

In a first stage of the process, a volume of powder feed material 34 ischarged into the powder feed material reservoir 18 and distributed overan upper surface of the building platform 16 to form a layer 36 of thepowder feed material 34. The powder feed material 34 may be distributedover the upper surface of the building platform 16, for example, by ablade 38. In addition, depending upon shape of the three-dimensionalobject 12 being formed and the stage of formation, the layer 36 of thepowder feed material 34 also may be distributed over a surface of one ormore layers of previously deposited unmelted powder feed material 39and/or over a surface of one or more previously deposited melted, fused,and solidified nitride, carbide, and/or boride material layers 40. InFIG. 1 , the layer 36 of the powder feed material 34 is distributed overthe upper surface of the building platform 16 and also over a surface ofmultiple previously melted, fused, and solidified nitride, carbide,and/or boride material layers 40.

The powder feed material 34 comprises at least one element that canreact with gaseous nitrogen, carbon, and/or boron to form a nitride,carbide, and/or boride compound or a nitrogen, carbon, and/orboron-containing solid solution. For example, the powder feed material34 may comprise a metal, e.g., iron (Fe) and/or titanium (Ti), and/or asemimetal (also referred to as a metalloid), e.g., silicon (Si). Suchmetals and/or metalloids may account for, by weight, greater than 90%or, more preferably, greater than 99% of the powder feed material 34.For example, in one form, the powder feed material 34 may comprise, byweight, greater than or equal to 99.8% iron. In some embodiments, thepowder feed material 34 also may comprise one or more nonmetals, e.g.,nitrogen, carbon, and/or boron. When present, the one or more nonmetalsmay account for, by weight, less than or equal to 10%, less than orequal to 5%, or, more preferably, less than or equal to 1% of the powderfeed material 34. In one specific example, the powder feed material 34may comprise, by weight, 99.95-99.99% iron and 0.05-0.01% nitrogen. Thepowder feed material 34 may have a mean particle diameter in the rangeof 1 micrometer to 100 micrometers and the layer 36 of the powder feedmaterial 34 may have a thickness in the range of 5 micrometers to 100micrometers.

After the layer 36 of the powder feed material 34 is distributed overthe building platform 16, selective regions 42 of the layer 36 arescanned by a high-energy laser beam 44. During the scanning process, thelaser beam 44 impinges the layer 36 and is advanced relative to a planedefined by an upper surface of the layer 36 along one or more predefinedtravel paths. The laser beam 44 may be a pulsed or continuous wave laserbeam having a power in the range of 100 W to 2000 W, a laser beam spotsize in the range of 50 μm to 250 μm, and a velocity in the range of 0.5meters per second to 10 meters per second.

As shown in FIG. 1 , the selective regions 42 of the layer 36 scanned bythe laser beam 44 correspond to a cross-section of the three-dimensionalobject 12 being formed. As best shown in FIG. 2 , as the laser beam 44scans the selective regions 42 of the layer 36, the laser beam 44impinges the layer 36 and heat generated by absorption of energy fromthe laser beam 44 initiates localized melting and fusion of the powderfeed material 34 within the selective regions 42 of the layer 36. As aresult, a pool 46 of molten feed material is created that fullypenetrates the layer 36 and extends through the layer 36 in a directionsubstantially perpendicular to the surface of the building platform 16(i.e., along the z-axis). As shown, the pool 46 of molten feed materialalso may extend at least partially into one of the underlying layers 40,for example, at a depth of less than 100 micrometers.

A volume of material underlying the pool 46 of molten feed material doesnot melt and is maintained in solid form at a temperature of less than500° C. as the laser beam 44 scans the selective regions 42 of the layer36. Depending upon shape of the three-dimensional object 12 being formedand the stage of formation, this volume of material underlying the pool46 may comprise a volume of unmelted powder feed material 39, a volumeof previously deposited melted, fused, and solidified nitride, carbide,and/or boride-containing material 40, and/or the building platform 16itself. As the laser beam 44 scans the selective regions 42 of the layer36 and is advanced relative to the upper surface of the layer 36 alongthe one or more predefined travel paths, the pool 46 of molten feedmaterial follows and leaves behind a trail of molten feed material inthe wake of the advancing laser beam 44. This molten feed material isquenched and rapidly solidifies by heat transfer from the pool 46 ofmolten feed material to the volume of solid material underlying the pool46. For example, the pool 46 of molten feed material may cool at a ratein the range of 10⁴ Kelvin per second to 10⁶ Kelvin per second in thewake of the advancing laser beam 44.

The pool 46 of molten feed material may be exposed to gaseous nitrogen,carbon, and/or boron as the laser beam 44 scans the selective regions 42of the layer 36 to respectively dissolve nitride, carbide, and/or borideions into the pool 46 of molten feed material. Dissolution of thenitride, carbide, and/or boride ions into the pool 46 of molten feedmaterial transforms the pool 46 into a molten nitrogen, carbon, and/orboron-containing solution. For example, in embodiments where the powderfeed material 34 comprises iron, the pool 46 of molten feed material maybe exposed to gaseous nitrogen to dissolve nitride ions into the pool 46and produce a molten solution of iron and nitrogen. Because the pool 46of molten feed material rapidly solidifies in the wake of the advancinglaser beam 44, the pool 46 of molten feed material is only exposed togaseous nitrogen, carbon, and/or boron for a brief duration prior tosolidification. For example, the pool 46 of molten feed material may beexposed to gaseous nitrogen, carbon, and/or boron for a duration of lessthan one second.

As shown in FIG. 1 , in one form, the pool 46 of molten feed materialmay be exposed to gaseous nitrogen, carbon, and/or boron by generating agaseous nitrogen, carbon, and/or boron-containing environment within thechamber 24. A gaseous nitrogen, carbon, and/or boron-containingenvironment may be generated within the chamber 24, for example, byintroducing a nitrogen, carbon, and/or boron-containing gas into thechamber 24 via the inlet 26. In one form, a gaseous nitrogen, carbon,and/or boron-containing environment may be generated within the chamber24 by introducing a solid nitrogen, carbon, and/or boron-containingmaterial into the chamber 24 and heating the solid material to releasegaseous nitrogen, carbon, and/or boron therefrom. In another form, asbest shown in FIG. 2 , the pool 46 of molten feed material may beexposed to gaseous nitrogen, carbon, and/or boron by locally directing astream of nitrogen, carbon, and/or boron-containing gas at a freesurface 48 of the pool 46. A stream of nitrogen, carbon, and/orboron-containing gas may be directed at the free surface 48 of the pool46, for example, by a nozzle 50. As the laser beam 44 scans theselective regions 42 of the layer 36 and is advanced relative to theupper surface of the layer 36, the nozzle 50 may be configured to tracka course that corresponds to the travel path of the laser beam 44 andthe pool 46 of molten feed material.

The nitrogen, carbon, and/or boron-containing gas introduced into thechamber 24 and/or directed at the free surface 48 of the pool 46 ofmolten feed material may comprise a nitrogen, carbon, and/orboron-containing compound that dissociates in the chamber 24 (forexample, upon contact with the pool 46 of molten feed material) toproduce nascent nitrogen (N), carbon (C), and/or boron (B), which canreadily diffuse into the pool 46 of molten feed material. Some examplesof nitrogen, carbon, and/or boron-containing compounds include urea(CO(NH₂)₂), ammonia (NH₃), nitrogen (N₂), and methane (CH₄). In someembodiments, the nitrogen, carbon, and/or boron-containing gas maycomprise a mixture of one or more nitrogen, carbon, and/orboron-containing compounds and an inert carrier gas (e.g., argon ornitrogen). The partial pressure of nitrogen, carbon, and/or boron at thefree surface 48 of the pool 46 of molten feed material and the durationof exposure thereto may be controlled or adjusted to achieve a desiredconcentration of nitrogen, carbon, and/or boron in the resulting pool 46of molten nitrogen, carbon, and/or boron-containing solution (and thusin the resulting bulk nitride, carbide, and/or boride material of thefinal three-dimensional object 12).

A relatively high-pressure environment (e.g., greater than 1 atmosphere)may be produced within the chamber 24 while the laser beam 44 isscanning the selective regions 42 of the layer 36, for example, toincrease the rate at which nitride, carbide, and/or boride ions diffuseinto the pool 46 of molten feed material. A relatively high-pressureenvironment may be generated within the chamber 24, for example, bycontrolling of the amount of gas introduced into the chamber 24 via theinlet 26 relative to the amount of gas discharged from the chamber 24via the outlet 30. For example, the environment within the chamber 24may be at a pressure in the range of 150 kPa to 150 MPa while the laserbeam 44 is scanning the selective regions 42 of the layer 36.

To promote the formation of nitride, carbide, and/or boride ions withinthe chamber 24 and dissolution of such ions into the pool 46 of moltenfeed material, in some instances, it may be desirable to employ a plasmaionization process. In such case, an electric field may be generatedwithin the chamber 24 to ionize the nitrogen-, carbon-, and/orboron-containing gas and transform the gas into a plasma state. Anelectric field may be generated in the chamber 24, for example, byestablishing an electric potential difference between the layer 36 ofthe powder feed material 34 and the chamber 24, which may accelerate thenitride, carbide, and/or boride ions in the ionized gas toward the pool46 of molten feed material. A subatmospheric pressure environment (e.g.,less than 1 atmosphere) may be established within the chamber 24 duringthe plasma ionization process, for example, by controlling of the amountof gas evacuated from the chamber 24 via the vacuum pump and evacuationsystem 32.

After the selective regions 42 of the layer 36 have been scanned by thehigh-energy laser beam 44, the laser beam 44 may be terminated. Upontermination of the laser beam 44, the pool 46 of the molten nitrogen,carbon, and/or boron-containing solution rapidly cools and solidifies toform another solidified nitride, carbide, and/or boride-containingmaterial layer that bonds with the previously solidified layers 40.Thereafter, the reservoir 18 may be raised in a build direction (i.e.,along the z-axis), or the building platform 16 may be lowered, by athickness of the newly solidified layer. Then, a further layer of powderfeed material 34 may be distributed over the surface of the buildingplatform 16 and over the previously solidified nitride, carbide, and/orboride material layers 40, scanned with the laser beam 44 in regionscorresponding to another cross-section of the three-dimensional object12, and solidified to form yet another solidified nitride, carbide,and/or boride material layer that bonds with the previously solidifiedlayers 40. This process is repeated until the entire three-dimensionalobject 12 is built up layer-by-layer. The resulting three-dimensionalobject 12 is of one-piece unitary construction and is made of a bulknitride, carbide, and/or boride-containing material. For example, thethree-dimensional object 12 may comprise a nitride, carbide, or borideof a metal or a metalloid, e.g., iron (Fe), titanium (Ti), or silicon(Si). Some examples of nitride, carbide, and boride-containing materialsinclude iron nitride, silicon nitride, titanium nitride, titaniumdiboride, and silicon carbide.

In one form, the three-dimensional object 12 may comprise a bulk ironnitride material having a relatively high concentration of nitrogen ions(e.g., greater than 10 at %) and exhibiting a magnetic Fe₁₆N₂ phase. Themagnetic Fe₁₆N₂ phase may exhibit a body-centered tetragonal (bct)crystal structure with space group I_(4/mmm) (#139), lattice constantsa=b=5.72 Å and c=6.29 Å, and a c/a ratio of 1.1. In one form, thethree-dimensional object 12 may be a permanent magnet and the magneticFe₁₆N₂ phase may account for, by volume, 50% to 100% of the bulk ironnitride material.

In another form, the three-dimensional object 12 may comprise a bulkiron (Fe), titanium (Ti), or silicon (Si)-based material having arelatively low concentration of nitride, carbide, and/or boride (e.g.,on an atomic basis, greater than 0% and less than or equal to 5%). Insuch case, the nitride, carbide, and/or boride ions may be dissolved insolid solution with the iron (Fe), titanium (Ti), or silicon (Si) andmay harden and/or help increase the strength of the bulk iron (Fe),titanium (Ti), or silicon (Si)-based material.

In one specific example, the powder feed material 34 may comprise analloy of iron (Fe) and 0.05 wt % to 0.4 wt % carbon (C), the pool 46 ofmolten feed material may be exposed to gaseous nitrogen or carbon, andthe resulting three-dimensional object 12 may comprise a bulk hardenedsteel that exhibits a body-centered cubic crystal structure or aface-centered cubic crystal structure and comprises, by weight, 0.01% to0.5% nitrogen and/or 0.1% to 4% carbon.

The repeated deposition, fusion, and solidification of layers of thepowder feed material 34 during formation of the three-dimensional object12 repeatedly creates thermal gradients within the nitride, carbide,and/or boride-containing material layers 40 in the build direction(i.e., along the z-axis) and produces local residual compressive andtensile stresses within the object 12 upon quenching of the pool 46 ofmolten feed material. As such, after formation, the three-dimensionalobject 12 may exhibit localized strains in the range of 0.5% to 1%. Theamount of strain present in the three-dimensional object 12 may betuned, for example, by controlling the thickness of each layer 36 ofpowder feed material 34 scanned by the laser beam 44, the mean particlediameter of the powder feed material 34, the shape of the particles thatmake up the powder feed material 34, and the power density, laser beamspot size, and/or velocity of the laser beam 44. In embodiments wherethe three-dimensional object 12 is made of iron nitride, the localresidual stresses within the object 12 may help promote formation andstabilization of a magnetic Fe₁₆N₂ phase within the object 12.

In some embodiments, the three-dimensional object 12 may comprise asolid exterior and a porous interior enclosed within the solid exterior(not shown). In such case, the porous interior of the object 12 may helpreduce the overall weight of the object 12 (as compared to embodimentswhere the object 12 is entirely solid). In one form, the porous interiorof the object 12 may comprise a multidimensional stochastic or periodicsupport structure, which may have closed or open interconnected pores.For example, the porous interior of the object 12 may comprise a two orthree-dimensional lattice support structure or truss including aplurality of repeating unit cells (e.g., a tessellation of one or moregeometric shapes) defined by a plurality of discrete segments connectedat their ends.

In embodiments where the three-dimensional object 12 comprises apermanent magnet exhibiting a magnetic Fe₁₆N₂ phase, the shape of thethree-dimensional object 12 may be configured so that the object 12exhibits certain desirable magnetic fields. For example, thethree-dimensional object 12 may be V-shaped, W-shaped, trapezoid-shaped,or helical in shape.

It may be desirable to perform a nitriding, carburizing, and/orboronizing treatment on the three-dimensional object 12 after formationthereof to increase the concentration of nitrogen, carbon, and/or borontherein. In such case, the three-dimensional object 12 may be heated toa temperature in the range of 450° C. to 550° C. while exposing one ormore surfaces of the three-dimensional object 12 to a nitrogen, carbon,and/or boron-containing gas at a pressure in the range of 200 kPa to 100MPa for a duration in the range of 1 hour to 30 hours to promotediffusion of nitride, carbide, and/or boride ions into the object 12. Tofurther promote diffusion of the nitride, carbide, and/or boride ionsthroughout a bulk of the object 12 (instead of only in an exteriorsurface portion of the object 12), one or more flow-through channels(not shown) may be formed within the three-dimensional object 12 duringmanufacture thereof. The one or more flow-through channels may bedefined by walls having wall surfaces that extend from an exteriorsurface of the object 12 and through an interior of the object 12. Theone or more flow-through channels increase the surface area of theobject 12 that can be exposed to the nitrogen, carbon, and/orboron-containing gas during the nitriding, carburizing, and/orboronizing treatment and also may allow exposure of the nitrogen,carbon, and/or boron-containing gas to an exterior surface portion aswell as an interior surface portion of the object 12.

In one form, the three-dimensional object 12 may comprise a bulk ironnitride material and a nitriding treatment may be performed on thethree-dimensional object 12 after formation thereof to increase theconcentration of nitrogen therein. In some embodiments, the nitridingtreatment may be performed to increase the concentration of nitrogenions within the iron nitride material to greater than 10 at % and topromote formation of a magnetic Fe₁₆N₂ phase within the iron nitridematerial. In such case, the object 12 may initially comprise an ironnitride material that exhibits a body-centered cubic crystal structure(e.g., ferrite) and/or a face-centered cubic crystal structure (e.g.,martensite), and the nitriding treatment may be performed to increasethe concentration of nitrogen ions within the iron nitride material andform a magnetic Fe₁₆N₂ phase exhibiting a body-centered tetragonal (bct)crystal structure within the iron nitride material.

The above description of preferred exemplary embodiments, aspects, andspecific examples are merely descriptive in nature; they are notintended to limit the scope of the claims that follow. Each of the termsused in the appended claims should be given its ordinary and customarymeaning unless specifically and unambiguously stated otherwise in thespecification.

What is claimed is:
 1. A method of manufacturing a three-dimensionalobject using a powder bed fusion additive manufacturing technique, themethod comprising: (a) providing a powder feed material including analloy of iron (Fe) and carbon (C); (b) distributing a layer of thepowder feed material over a solid substrate; (c) scanning selectiveregions of the layer of the powder feed material with a laser beam tolocally melt the selective regions and form a pool of molten feedmaterial, the selective regions of the layer corresponding to across-section of a three-dimensional object being formed; (d) exposingthe pool of molten feed material to gaseous carbon and gaseous nitrogento dissolve carbide ions and nitride ions into the pool of molten feedmaterial to produce a molten carbon and nitrogen-containing solution;(e) terminating the laser beam to cool and solidify the moltencarbon-containing solution into a solid layer of hardened steel; and (f)repeating steps (b) through (e) to form a three-dimensional object madeup of a plurality of solid layers of hardened steel, wherein theplurality of solid layers of hardened steel comprise, by weight, 0.1% to4% carbon and 0.01% to 0.5% nitrogen, and wherein the plurality of solidlayers of hardened steel exhibit a body-centered cubic crystal structureor a face-centered cubic crystal structure.
 2. The method of claim 1wherein the powder feed material comprises, by weight, 90% to 99.6% iron(Fe) and 0.05% to 0.4% carbon (C).
 3. The method of claim 1 wherein thepowder feed material includes at least one nonmetal element selectedfrom the group consisting of nitrogen, carbon, or boron, and wherein theat least one nonmetal element accounts for, by weight, greater than 0%and less than or equal to 5% of each particle of the powder feedmaterial.
 4. The method of claim 1 wherein step (d) includes: directinga gas stream at the pool of molten feed material, wherein the gas streamcomprises at least one of urea (CO(NH₂)₂), ammonia (NH₃), nitrogen (N₂),or methane (CH₄).
 5. The method of claim 1 wherein steps (b) through (f)are performed within a chamber, and wherein step (d) includes:introducing a carbon and nitrogen-containing gas and optionally aboron-containing gas into the chamber; and establishing a high-pressureenvironment within the chamber, the high-pressure environment exhibitinga pressure in the range of 150 kPa to 150 MPa.
 6. The method of claim 1wherein steps (b) through (f) are performed within a chamber, andwherein step (d) includes: introducing a carbon and nitrogen-containinggas and optionally a boron-containing gas into the chamber; generatingan electric field within the chamber to ionize the carbon andnitrogen-containing gas and the optional boron-containing gas andtransform the gas into a plasma; establishing a subatmospheric pressureenvironment within the chamber; and establishing an electric potentialdifference between the solid substrate and the plasma to attractnitrogen ions, carbon ions, or boron ions to the pool of molten feedmaterial.
 7. The method of claim 1 wherein, when the selective regionsof the layer are scanned with the laser beam, a volume of solid materialunderlying the selective regions of the layer does not melt and ismaintained at a temperature less than 500° C., wherein, upon terminationof the laser beam, the pool of molten feed material is quenched by heattransfer from the pool of molten feed material to the volume of solidmaterial underlying the selective regions of the layer, and wherein,upon termination of the laser beam, the pool of molten feed material iscooled at a rate in the range of 10⁴ Kelvin per second to 10⁶ Kelvin persecond.
 8. The method of claim 1 wherein, during formation of theplurality of solid layers of hardened steel, thermal gradients arerepeatedly generated within the solid layers such that thethree-dimensional object made up of the plurality of solid layersexhibits localized regions of residual stress.
 9. The method of claim 1wherein the powder feed material comprises, by weight, greater than orequal to 90% iron (Fe).
 10. A method of manufacturing athree-dimensional object using a powder bed fusion additivemanufacturing technique, the method comprising: (a) providing a powderfeed material including an alloy of iron (Fe) and carbon (C); (b)distributing a layer of the powder feed material over a solid substrate;(c) scanning selective regions of the layer of the powder feed materialwith a laser beam to locally melt the selective regions and form a poolof molten feed material, the selective regions of the layercorresponding to a cross-section of a three-dimensional object beingformed; (d) exposing the pool of molten feed material to gaseousnitrogen or carbon to respectively dissolve nitride or carbide ions intothe pool of molten feed material to produce a molten nitrogen orcarbon-containing solution; (e) terminating the laser beam to cool andsolidify the molten nitrogen or carbon-containing solution into a solidlayer of hardened steel; and (f) repeating steps (b) through (e) to forma three-dimensional object made up of a plurality of solid layers ofhardened steel, wherein the hardened steel exhibits a body-centeredcubic crystal structure or a face-centered cubic crystal structure andcomprises, by weight, 0.1% to 4% carbon and 0.01% to 0.5% nitrogen. 11.The method of claim 10 wherein step (d) includes: directing a gas streamat the pool of molten feed material, wherein the gas stream comprises atleast one of urea (CO(NH₂)₂), ammonia (NH₃), nitrogen (N₂), or methane(CH₄).
 12. The method of claim 10 wherein steps (b) through (f) areperformed within a chamber, and wherein step (d) includes: introducing anitrogen or carbon-containing gas into the chamber; and establishing ahigh-pressure environment within the chamber, the high-pressureenvironment exhibiting a pressure in the range of 150 kPa to 150 MPa.13. The method of claim 10 wherein steps (b) through (f) are performedwithin a chamber, and wherein step (d) includes: introducing a nitrogenor carbon-containing gas into the chamber; generating an electric fieldwithin the chamber to ionize the nitrogen or carbon-containing gas andtransform the gas into a plasma; establishing a subatmospheric pressureenvironment within the chamber; and establishing an electric potentialdifference between the solid substrate and the plasma to attractnitrogen ions or carbon ions to the pool of molten feed material. 14.The method of claim 10 wherein, when the selective regions of the layerare scanned with the laser beam, a volume of solid material underlyingthe selective regions of the layer does not melt and is maintained at atemperature less than 500° C., and wherein, upon termination of thelaser beam, the pool of molten feed material is quenched by heattransfer from the pool of molten feed material to the volume of solidmaterial underlying the selective regions of the layer.
 15. The methodof claim 10 wherein, upon termination of the laser beam, the pool ofmolten feed material is cooled at a rate in the range of 10⁴ Kelvin persecond to 10⁶ Kelvin per second.
 16. The method of claim 10 wherein,during formation of the plurality of solid layers of hardened steel,thermal gradients are repeatedly generated within the solid layers suchthat the three-dimensional object made up of the plurality of solidlayers exhibits localized regions of residual stress.
 17. The method ofclaim 10 wherein the powder feed material comprises, by weight, 90% to99.6% iron (Fe) and 0.05% to 0.4% carbon (C).
 18. The method of claim 10including: after step (f), exposing the three-dimensional object togaseous nitrogen, carbon, or boron to increase the respectiveconcentration of nitrogen, carbon, or boron within the solid layers ofhardened steel.
 19. The method of claim 10 wherein the powder feedmaterial comprises, by weight, greater than or equal to 90% iron (Fe).